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Sai Phanindra

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Sai Phanindra last won the day on November 26 2015

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  1. Hi, I tried giving the additional mass and inertia to the global rigid body. However, during the RIGID BODY INITIALIZATION of the global rigid body (in _0000.out), the added mass and inertia are ignored and only the slave node mass is considered. Is there any workaround where I can add mass and inertia externally? Also, I am facing another problem with global rigid body: The model is initially off the ground, so the global rigid body is activated. Once it reaches the ground after free fall phase, the global rigid body is turned off and the computation is carried out as expected (with a lower time step and all elements active) for 30 ms. Beyond that, the error (which is -5% at this point) starts increasing and reaches +99% at which point the dynamics become nonphysical. i.e. the kinetic energy of the system increases to 10,000 J even though the initial total energy of the system is 460 J. Is there any reason for this sort of instability?
  2. Hi, I have checked and compared the .out files for the model with and without global rigid body. The model with global rigid body does not account for the added inertia.
  3. Hi, I have added mass and Inertia at the CG of the system, which I want to retain with the global rigid body. My analysis involves impact of a body on hard ground and the objective is to predict the subsequent dynamics. For the same, I want to use a global rigid body to reduce the time taken during the bouncing phase.
  4. Hi Gopal, Thanks for the info. It would be great if you could elaborate the following: 1. Suppose I add some external inertia to one of the rigid bodies which are deactivated during free-fly, What happens to the inertia? Is it also deactivated. 2. If that is the case, can I add external inertia to the global rigid body to compensate for the deactivated Inertia? Thanks, Sai
  5. Hi, I am trying to run a dynamic impact analysis problem with bouncing involved. In my model, I have added inertia specified in global skew frame to replicate the actual case. I want to reduce the computation time when the body is off the ground by introducing a rigid group consisting of all the nodes in the model. For the same, I am using a sensor of TYPE: interface. According to the RBODY definition, is SENS_ID is non-zero, the added inertia is ignored. Please confirm if this is true? If so, how do I ensure that the added inertia is incorporated in the model when I make SENS_ID non-zero. Thanks and Regards, Sai Phanindra
  6. Hi, I am using INTER/TYPE7 for contact definition of a piston sliding inside a cylinder. The contact parameters are: Istf=4, Igap=1, FRIC=0.1, gapmin=0.01, INACTI=6, Ifric=0, Iform = 2. Please find attached the Resultant normal force and the Resultant Tangential force plot (created by TH/INTER output block). As it can be observed from the plot, the peak normal force is ~12 KN for which the expected tangential force should be 1.2 KN (for mu=0.1). However, the observed resultant tangential force peak is upto ~3 KN. Please resolve this problem. Thanks a ton. Regards, Sai Phanindra
  7. Hi Prakash, I know the value of thermal expansion coefficient (alpha). Can you guide me how it converts to the temperature exponent in LAW2? Thanks, Sai
  8. Hi, I want to do a thermal analysis using RADIOSS, as it involves impact as well. In optistruct, I have done the thermal analysis using MAT1 wherein I specified the thermal expansion coefficient (A). What material should I use in RADIOSS and how can I specify the thermal expansion coefficient. Thanks and Regards, Sai Phanindra
  9. Hi Prakash, I am trying to model soil in RADIOSS and I have used the equations as given above to find the yield coefficients A0, A1 and A2. The results I am getting are different from the actual properties. Can you give more insight on how J2 coefficients are calculated. I am unsure of the equation you have given for J2 because the curve given below (J2 vs P curve) can never occur for equation given by J2 = 1/3*(alpha^2*P^2- 2alpha^2*t0*P/tan(alpha) + alpha^2*t0^2/tan^2(alpha), since the P^2 coefficient is positive. Also, Is J2' the same as J2 in that text? Also, Can you kindly guide what property to use for modeling soil in RADIOSS. I am currently using P14_SOLID with Isolid=24 and ismstr = 10. Please let me know if there is any better property. Further, is it advisable to have coarse mesh or fine mesh for modeling soil?
  10. Hi Prakash, Can you please let me know the reference for the below mentioned image which contains the information on how to find the A0, A1 and A2 parameters for LAW10.
  11. Hi, I am using RADIOSS Block 120 solver. I have defined a point mass (elem type M). How can I define moment of Inertia for the point mass. I couldn't find any options to do so in CARD EDIT. Thanks.
  12. Hi, I am facing a similar error. My model was working fine until I deleted the mesh for a component and remeshed it. I am now getting he following error: ERROR ID: 78 ** ERROR : UNDEFINED NODE NUMBER DESCRIPTION: IN NODE GROUP DEFINITION DEFINITION : NODE ID = 2096 DOES NOT EXIST I have deleted the empty contact surfaces and sets. I am unsure what I can do now to resolve the error.
  13. Hi Prakash, Thanks for your suggestion. I checked the material model. The problem was with the definition of stress-strain curve. I had previously defined Stress vs. total strain (elastic + plastic) but now I have changed it to Stress vs. Plastic strain and the model is now working fine. Thanks again for your help... You are awesome man. Keep rocking .
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